#include<iostream>  
#include<cstdio>  
using namespace std;  
int main()  
{  
      
    int n,i,sum;  
      
    while(scanf("%d",&n)!=EOF)  
    {  
        sum=0;  
        for(i=1;i<=n;i++)  
        sum+=i;  
        printf("%d\n\n",sum);  
          
          
    }  
    return 0;  
 }